Troubleshooting Communications Under Windows 3.0
ID: Q82136
|
The information in this article applies to:
-
Microsoft Windows versions 3.0, 3.0a
SUMMARY
The following table depicts the standard settings for the four
communications ports that Microsoft Windows version 3.0 and Microsoft MS-
DOS version 4.01 support. This information is useful for troubleshooting
communications problems under Windows 3.0.
A brief description of each column appears below the table. NOTE: In the
table below, Windows 3.0 is abbreviated as WIN3.
WIN3 COMM.DRV WIN3 Default WIN3 Desired
Procom Plus SYSTEM.INI Settings SYSTEM.INI Settings
Port I/O Range IRQ I/O Range I/O Range
---- ----------- --- ------------------- ------------------
[386Enh] [386Enh]
COM1 3F8h 4 COM1BASE=3F8h COM1BASE=3F8h
COM2 2F8h 3 COM2BASE=2F8h COM2BASE=2F8h
COM3 3E8h 4 COM3BASE=2E8h COM3BASE=3E8h
COM4 2E8h 3 COM4BASE=2E0h COM4BASE=2E8h
The first column lists the ports. The second column describes the settings
for the ports that both the Windows COMM.DRV and most popular
communications packages use by default. The third column shows what Windows
3.0 sets by default and the fourth column shows what should be set in the
[386Enh] section of the SYSTEM.INI file for proper functioning of the ports
under 386 enhanced mode Windows 3.0.
NOTE: The default values specified for COM3 and COM4 ensure PS/2
compatibility.
There is a problem with using the Windows 3.0 SYSTEM.INI file setting
COM(x)IRQ= in the [386Enh] section. Changing the COM port interrupt is NOT
be recognized by Windows applications. However, MS-DOS applications running
with Windows 3.0 in 386 enhanced mode do recognize this COM(x)IRQ= setting.
Therefore, Windows applications that use the COM ports are limited to
hardware interrupts 3 and 4 for COM2 and COM1, respectively.
MORE INFORMATION
In 386 enhanced mode, Windows 3.0 accesses the communication ports using a
device called the virtual communications driver (VCD). MS-DOS applications
running from Windows in 386 enhanced mode access COM ports by using the
VCD. Changing the COM(x)IRQ= setting in the SYSTEM.INI file allows the use
of a COM port that has been set to a different hardware interrupt, but this
works only for MS-DOS applications running in 386 enhanced mode.
Windows applications use the VCD as well; however, they must also
communicate through a second layer, the Windows real/standard mode COMM
driver. The real/standard mode COMM driver does not recognize changes made
to the VCD; therefore, Windows applications cannot use COM ports assigned
to any interrupts other than industry standard ones.
The following information about COM(x)IRQ is from the SYSINI2.TXT file:
COM1Irq=<number>
COM2Irq=<number>
COM3Irq=<number>
COM4Irq=<number>
Default: COM1Irq=4; COM2Irq=3; COM3Irq=4; COM4Irq=3
Purpose: Specifies which interrupt line is being used by
the device on the specified communications port.
Check your hardware documentation for the
appropriate value. Setting a value to -1 disables
input for that COM port. You would do this only
if there is a hardware conflict between ports.
Microsoft has confirmed this to be a problem in Microsoft Windows
version 3.0. We are researching this problem and will post new
information here as it becomes available.
Troubleshooting Communications Problems Under Windows 3.0
- You can simultaneously use two communication ports that share the
same interrupt (for example, COM1 and COM3, or COM2 and COM4) only if
the hardware is capable of doing so. The ability to share
communications port interrupt request lines (IRQs) is hardware
dependent. Currently, the only hardware that you can be sure that IRQ
sharing is supported on is Micro Channel Architecture (MCA) hardware.
Although Extended Industry Standard Architecture (EISA) hardware does
have IRQ sharing as part of its specifications, implementation on
current machines is random. If you cannot successfully share an IRQ
with the COMIrqSharing switch set to true, the hardware does not
support IRQ sharing and Windows 3.0 is not able to overcome the lack
of support for this feature using software.
Note: On some implementations of EISA, there is some configuration of
the system hardware that must take place before IRQ sharing can occur.
An example of this is Compaq's EISA machines. By default, they are
not configured to IRQ share. Be aware that you may need to take
additional steps to configure such machines.
- COM3 and COM4 may not be reliable under Windows 3.0 (in standard or
real mode) unless both COM1 and COM2 are first activated. If you use
only COM3 and/or COM4, you may experience problems (with printing,
communications, or your mouse). If you use COM1 and COM3 without using
COM2, you also may have problems. The easiest way to remember this is
to not use a higher serial port (2, 3, or 4) unless all lower number
ports (1, 2, and 3) are first activated (or in use).
- Standard and real mode Windows 3.0 use COMM.DRV directly, whereas
386 enhanced mode Windows 3.0 serializes the ports using the VCD.
For this reason, serial communication can theoretically be
considered more reliable under standard and real mode because there
can be no miscommunication between the VCD and COMM.DRV. In cases
where you are using multiple communications ports under Windows 3.0
386 enhanced mode, verify that the base port addresses are set as
described in the table earlier in this article.
NOTE: IRQ sharing is possible under 386 enhanced mode Windows 3.0 only
if you make the necessary changes to the [386Enh] section of the
SYSTEM.INI file as outlined above.
Additional query words:
tshoot 3.00 3.0 3.0a 3.00a
Keywords :
Version : WINDOWS:3.0,3.0a
Platform : WINDOWS
Issue type :
|